Hello everyone,
I have been testing UCS in Cassandra 5 and noticed that the behavior of major
compaction diverges from the documentation.
Since I am using the default value of base_shard = 4, I expected 4 compaction
tasks to be initiated.
However, in my case only a single task was launched, and it included all
SSTables in the table.
My compaction settings: { 'base_shard_count': ‘4', 'class':
'org.apache.cassandra.db.compaction.UnifiedCompactionStrategy',
'scaling_parameters': ‘T4' }
Documentation excerpt below:
Major compaction
Under the working principles of UCS, a major compaction is an operation that
compacts together all SSTables with (transitive) overlap, and whose output is
split on shard boundaries appropriate for the expected resulting density.
In other words, a major compaction will result in b concurrent compactions,
each containing all SSTables covered in each of the base shards. The output
will be split on shard boundaries whose number depends on the total size of
data contained in the shard.
